Rapid sintering protocol produces dense ceria‐based ceramics

Abstract

We report on a rapid sintering protocol, which optimizes the preparation of 0‐29 mol% Gd‐doped ceria ceramics with density ≥98% of the theoretical crystal lattice value. The starting material is a nanometer grain‐sized powder prepared by carbonate co‐precipitation and calcined with minimal agglomeration and loss of surface area. Slow (5°C/min) heating of the green‐body from 500°C to the optimum temperature of rapid sintering (T1opt, dwell time <1 minute) followed by 20°C/min cooling to 1150°C with 6 minutes dwell time, produces maximum pellet density. T1opt increases from 1300 to ~1500°C with increase in Gd‐content, while the average grain size in the maximally dense pellets, as determined by scanning electron microscopy, ranges between 600 nm and ~1 μm. For each doping level, the logarithm of the average grain size decreases linearly with 1/T1. By avoiding extended exposure to sintering temperatures, this protocol is expected to minimize undesirable Gd segregation.

Dopant Concentration Controls Quasi-Static Electrostrictive Strain Response of Ceria Ceramics

“…The pellet density was measured by the conventional Archimedes method ( Figure 2 ). 28 At 25 mol % doping and below, the porosity (1 – density measured /density theoretical ) of both Sm- and Gd-doped pellets was <4%. Sample pellets were polished; top and bottom faces were made parallel with silicon carbide polishing papers (up to 1600 mesh) and then washed with 100% ethanol in an ultrasonic bath for 30 min to remove silicon carbide residue.…”

“…Gd x Ce 1– x O 2– x /2 (0 ≤ x ≤ 0.25) powders were synthesized by a coprecipitation method. 28 A 0.7 M aqueous solution of (NH 4 ) 2 CO 3 (99% extra pure, Arcos Organics) was added dropwise to an aqueous solution containing the amounts of Gd(NO 3 ) 3 ·6H 2 O and Ce(NO 3 ) 3 ·6H 2 O (0.3 M, total solute, purity 99.9%, Strem) required to provide the Gd concentrations desired. This mixture was kept at 80 °C under continuous stirring for 1 h. The precipitates were then collected by centrifugation, washed three times with water and then with ethanol, and afterward allowed to dry at 120 °C for 12 h. The resulting powders were ground, sifted through a 50 μm mesh, and calcined in air at 495 °C for 2 h. Cylindrical pellets were then formed by cold isostatic pressing of the powders at 300 MPa, followed by rapid sintering, with optimal temperatures and times as reported in refs ( 21 and 28 ).…”

“… Ceramic pellet porosity, (1 – density measured /density theoretical ), determined by the Archimedes flotation method, described in ref ( 28 ) as a function of dopant concentration. A single 5 mol % Sm-doped ceria pellet (Sm small) was prepared according to the protocol described for GdDC pellets.…”

Single‐step densification of nanocrystalline CeO2 by the cold sintering process

“…These high processing temperatures generally yield increased diffusion and importantly also segregation of the rare‐earth dopant . A rapid sintering protocol was recently proposed to obtain dense ceria‐based ceramics and avoid undesirable Gd segregation commonly encountered …”

“…[12][13][14] A rapid sintering protocol was recently proposed to obtain dense ceria-based ceramics and avoid undesirable Gd segregation commonly encountered. 15 In addition, many efforts have been applied to lower the sintering temperature of CeO 2 and its corresponding doped counter parts. Sintering techniques such as pulse electric current sintering, spark plasma sintering, two step sintering, and flash sintering, among others have been used.…”